There has rapidly been increased requirements for the development of a large capacity-information transmission along with the recent wide spread of personal computers and the internet. For this reason, it has been desired for the spread of the optical transmission, which can ensure a high transmission rate, even to the terminal information transmission devices such as personal computers. To realize this, it is necessary to mass-produce high quality optical waveguides for use in the optical interconnection, at a low production cost.
As materials for preparing such an optical waveguide, there have been known, for instance, inorganic materials such as glass and semiconductor materials and various resins. When it is intended to prepare an optical waveguide using a resin, film-forming processes required can be conducted by coating and heating operations under the atmospheric pressure and accordingly, this method is quite advantageous in that devices and processes to be used are quite simple. Various kinds of resins have been known as those which permit the constitution of an optical waveguide and, in particular, polyimides have been expected as such materials because of their high glass transition points (Tg) and excellent heat resistance. When preparing an optical waveguide using a polyamide resin, the resulting waveguide may ensure long-term reliability and it can withstand the soldering.
An optical device prepared using a resin such as an optical waveguide is in general constructed by forming V-shaped grooves for mounting optical fibers on a substrate such as a silicon wafer and subsequently laminating, in order, a lower clad layer, a core layer and an upper clad layer of resins. For instance, a silicon wafer having a diameter of about 12.7 cm is prepared as a substrate; a large number of optical elements such as optical waveguides are lengthwise and crosswise formed and arranged on the substrate; a dicing tape is adhered to the back face of the same; and the silicon wafer is diced with a blade to thus separate the wafer into individual optical devices. Thus, desired optical waveguide devices can be mass-produced.
When applying a dicing tape onto the back face of the substrate and carrying out the dicing with a blade to thus separate optical devices by a single dicing operation or stage, however, a problem arises such that the substrate, in particular, the edge of the back face thereof is ruptured. In this connection, there has been proposed a method in which the upper resinous portion is cut using a relatively soft blade, while the lower substrate portion is cut using a relatively hard blade. However, this method suffers from such problems that it requires the use of two kinds of blades and that steps are formed at the cut area due to the use of such two kinds of blades. Furthermore, both of these methods suffer from a problem in that the substrate and, in particular, the edge of the back face thereof is ruptured when peeling off the dicing tape. The problem of such ruptures may further results in various other problems. For instance, the ruptures of the edge portion result in the lost of the flatness of the resulting optical device and the broken pieces of such edge portion serve as foreign substances and they adversely and variously affect the optical device.